Electrical measuring instrument.



' PATBNTED NOV. 6, 1906.

E. F. NORTHRUP. ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED MAY28, 1908.

2 SHEETS-SHEET 1.

Z wmwhoz No. 835,461. PATENTED Nov. 6, 1906.

' E. F. NORTHRUP. 4

ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED MAY 26. 1906.

2 SHEETS-SHEET 2.

54 25 39 29 55 47 56 5 2 4'17 7 1d Z2 Z4 57 711 V l 114 4 K5 46 4 I :lJ0

witweoow UNI-TED STATES PATENT ;-.oEEro EDWiN E. NORTHRUP, 0EPHILADELPHIA, PENNSYLVANIA, AssIGNoR To THE LEEDS & NORTHRUP COMPANY, orPHILADELPHIA, rENNsYn VANIA, A CORPORATION or PENNSYLVANIA.

ELECTRICAL MEASURING INSTRUMENT. I

To all whom it may concern: Be it known that I, EDWIN F. Nonr' RUP, acitizen of the United States, residing at Philadelphia, in the county ofPhiladelphia and State of Pennsylvania, have invented certain new anduseful Improvements in Electrical Measuring Instruments, of which thefollowing is a specification.

,-This invention relates-more especially to.

comes a deflection-ohmmeter, or the ratio .may be that of a resistancewhich changes with temperature to a fixed resistance when .theinstrument becomes a direct-reading instrument for the measurement oftemperatures.

The instrument may also be used to measure other quantities. a

In order to more fully describe my said invention, reference will be hadto the accom- .panying drawings, in which- Figure 1 represents a to planview, with a portion of the cover bro en away, of one form of instrumentembodying my present invention; Fig. 2, an enlarged fragmentary frontelevation of magnet and moving sys-' tem of said instrument ,Fig. 3, acentral vertical section of saidinstrument; Fig, 4, a front elevationof, the moving system removed from the instrument Fig. 5, a'top planview of said system; Figs. 6, 7, and 8, diagrammatic views to illustratethe principle and operation of the instrument, and Fig.9 a diagram toillustrate the application of the instrument to the measurement oftemperatures. y I will first describe a specific form of the instrumentand then take up the theory of its operation.

Referring to the accompanying drawings, 1 represents the permanentfield-magnet, preferably of cast-iron, to the pole ends of which aresecured, as by means of screws 2 2', plates 3 and 1, preferably ofNorway iron. Secured, respectively, to the plates 3 and 4 are twocrescent-shapedpole-pieces 5 and 6, also Specification offLettersfatenti Application filed May 26,1QM5. Serial o. 318,851.

Patented Nov, 6, 1906.

preferably of Norway iron. These crescent shaped ole-pieces are locatedone directly above t e other,'leaving a sufficient space secured toopposite poles of the magnet 1, one of these crescent-shapedpole-piecesis of north polarity and the other of south polarity. Poleieces of othershapes which will produce t e desiredform offield may be substituted forthe specific form herein shown without departin from the s hit of myinvention as views in its broa er aspect.

The moving system comprises two flat coils 7 and 8, mountedv in adamping-frame consisting of two preferably aluminium plates 9' and 10,having open wings 11 and 12, adapted to inclose the respectivepole-pieces 5 and 6 when the system is'in position with out engaging thesame.- (See Fig. 2.) The 'there'between for the moving systermf Beingsystem thus damped is practically dead-beat.v

The damping-frame and coils are mounted upon a shaft 13, which passesthrough the said frame intermediate of the coils. shaft is provided witha flanged portion or collar 14, which, together with a flanged nut 15,screw-threaded on the shaft,'form clamping means to hold the plates-9and 10m posi- This tion and to clamp the coils therebetween.

The shaft 13- is rovidedwith hardened pivot-points 16 and 17 at itsrespeetive ends mounted, respectively, in jeweled bearings 18 and 19,carried by adjusting-screws 20 and 21. The screw 20 is carried in aplate 22, adjustably secured to the top of the magnet 1 by means ofscrews 23, passing through slots24 in said plate. The screw 21 iscarried 'in a similar plate 25, adjustably secured to the lower face ofthe magnet 1 by means ofscrews 26, passing through slots 27 in said pate.

The pivotal bearings of the shaft 13 are so located that the axis ofrotation for the moving system approximately coincides with the centerof the arcs forming the outside edge of the crescent-shaped pole-piecesthat is the axis of rotation of said'system should coincideapproximately with the point 2,, Fig. 6.- By means of the adjustableplates 22 and 25 the position of the axis may, however, be varied. Thereason for this will hereinafter more fully appear. With the system thusmounted one coil will move so as to get more get more from under saidpole-pieces as the system rotates.

balance-Weights 32 and Upon the upper end of the shaft 13 is rigidlymounted a small ring 28, which when the system is in position inclosesthe upper pivot-bearing. Secured to the top of this ring is a pointer orindex 29, preferably of aluminium or other very light material, whichmay be sore -threaded, as at 34, upon which portion it may be made tocarry one or more compensating weights, as the Weight 35. Screw-threadedrods 30 and 31, the latter carrying screw threaded compensating 33,respectively, may also be mounted on the ring 28 for the purpose ofbalancing the system.

The pointer 29 is adapted to move over a scale 36, mounted upon asegmental plate 37,

' which may in turn be'mounted on supports be laid off on an arc struckwith the axis of- 38, carried upon the upper face of the magnet. Thegraduations of this scale will of course depend upon the quantity whichthe instrument is designed to measure. In the drawings a scale is shownlaid off in ohms. If the instrument is to be used in measuringtemperatures, the scale would be laid on" in degrees of temperature, andso on, as the case may be.' In any event the scale would rotation of themoving system as the center.

The angular movement of the pointer 29 may be limited by two small wirestops 39 and 40, which may be the ends of a small wire 41, secured to ascrew 42, screwed into the top of the ma et.

While I have erein shown a pointer instrument, I do not wish to beunderstood as limiting my invention to this specific type. Moreover, Ido not wish to be understood as confining my present invention to thespe.

cific construction and mounting ofthe movable system herein shown.

The magnet 1 is mounted fast upon a pref erably wooden base'43, having acut-away portion 44, over-which extends the ends of the magnet carryingthe moving system. This base constitutes a false bottom adapted to restupon a real bottom or base 45, to which it may be secured in anysuitable way.

Adapted to inclose the magnet, the moving system, pointer, and scale isa preferably metal cover 46, having an elongated opening 47, adapted toregister with the scale. Back of this opening is secured. a glass plate48. v

The cover 46 rests upon the base 43 and may be held down upon the same'by means of countersunk screws 49, which engage lugs 50, secured to theinside of said cover.

7 I The electrical connections of the system are as follows: The coils 7and 8 in the form shown are wound in the form of two bobbins with opencenters and when vie'wflfrom the same flat side are wound in the samedirection, so that corresponding flat sides of said coils-will-have likepolarity. The inner tercease].

are preferably fine silver wires and: so very delicate that theirmechanical or torsional efifect on theangular movement of the sys ternis negli ible, so that the system may be freely mova 1e.

Mounted upon the base 43 are four binding-posts 58, 59, 60, and 61. Thebindingpost 58 is connected to the terminal 53 by conductor 62, thebinding-post 59' is connected totheterminal 56 through the resistance 66by means of conductor 64, the binding-post 60 is connected to theterminal 57 by conductor 63, and the binding-posts 59 and 61 areelectrically connected by conductor 65, all of which conductors may becountersunk in base 43. In series with the conductor 64 is mounted aresistance-coil 66, the function of which will hereinafter more fullyappear. This coil 66 may also be countersunk in a recess cut in the base43.

Bindin -posts 58 and 59 are for connection to t e source ofelectromotive force, while bindingosts 60 and 61 are for connection tothat which has to be measured. For the purpose of indicating how theseconnections are to be made Tmay provide indicating-buttons marked BA,and X.

The theory of the instrument is as follows: Referring to the diagramFig. 8, let T, represent the resistance of the coil '8, having n, turnsof wire, and r, the resistance of the coil 7, having n, turns of wire;also, sent the flux of the field throu H the flux of the field throu h te coil 7, and I and I, the current strengt sin the respective coils 8and 7. Let R equal the resistance of a coil 58 of fixed value, at theresistance of a coil X of unknownvalue, and E an electromotive forceapplied between the coils and resistances, as shown. Then when thesystem has moved to a position of equilibrium l l l z' z zi let H reprehthe coil 8,

but, according Ohms law,,,zIa: E and Substituting the values ofiii andI2 in tbe above equation e have a; z H271/2 In practice in m and m 022.Therefore as I R, when w R or H296 111R.

The system will therefore be in rotational equilibrium when H m- -H R;but in order for this to be true the system must be capable of moving insuch manner and the magnetic fields acting thereon must be so disposedor arranged that as coil 7 gets into more of the field or includes anincreasing number of lines of force the coil 8 must move into less of afield or must include a decreasing number of lines of force, or viceversa. This is accomplished by mounting the coils for movement in afield which in the instrument shown is produced by the crescentshapedpole-pieces 5 and 6, (see also Fig. 6,) in which the coils are indicateddiagrammatically in dotted lines. In Fig. 6, let the point 2, representthe center of the outer arc of the crescent-shaped pole-piece and z, thecenter of the inner arc thereof. It is evident that if coils 7 and 8,rigidly connected by a frame, rotate through a small angle in the planeof the paper on 2 as a center these coils will remain equally under thepolepiece. If, however, they rotate on the point 2 as a center by aclockwise rotation coil 7 will move more and more under the polepiece,while the coil 8 will move more and more from under the pole-piece, andvice versa, for anticlockwise rotation. Thus the effective field offorce acting on coils 7 and 8 changes with the rotation thereof. The

nearer the center of rotation approaches the 4 point 2 the greater mustbe the angle of deflection to change by a given amount the ratio H1 2rotation of the system near point 2 opens the scale, while bringing thesaid center of rotation nearer point z, closes the scale. Now ifcurrents flow through both coilsand in such a direction as to cause bothcoils to try-to move from under the pole-pieces the Hence bringing thecenter of system will seek a position of equilibrium,

which is independent of the actual value of the currents flowing andwhich depends only upon the ratio of the portions of the main current,which divides to flow in the two coils.

forces acting ecome nil, the system must be in neutral equilibrium inrespect to angular movement. The instrument, therefore, as used asaratio instrument is essentlally not a torsional-spring instrument. Theleadingin wires, therefore, are made so delicate that they exercise anegligibly small control as compared with the control of the magneticforces.

It will be seen by a reference to diagram Fig. 8 and in view of theforegoing explana-' tion that by connecting a resistance between points56 and 59, for example, of fixed value the instrument will measure theratio of value of its resistance to that of a resistance or theequivalent thereof of unknown value connected between the points 60 and61, for example. Then by calibrating the scale for different positionsof the index to correspond to different values of X the instrumentbecomes direct reading.

If X be the resistance-wire of an electric thermometer, the differentvalues of resistance of this wire under various degrees of heat may belaid off on the scale in degrees of temperature when the instrumentbecomes a direct-reading instrument for the measureof coil X to coil 58,or where as equals resistance of coil X and R the resistance of coil 58.Also since 67 on the a: side may be equal in resistance to the wire 69on the R side this arrangement practically compensates for changingresistance in the thermometer-leads. This is an extremely simple andefficient way of reading tem eratures, as the readings are practicallyin ependent of the variations in the current used.

An instrument of the kind herein described will operate for temperaturemeasurements on three or four series-connected dry cells or 'may be usedwith a commutated current. from a hand-magneto. The instrument used inthis capacity is especially valuable for rapidly taking the high andoften variable temperatures of furnaces and. the likes.

What I claim is- 1. An electrical measuring instrument, comprising amagnet, a moving system comprising a plurality of current-carrying coilsmechanically free to move in the field of said magnet in such a mannerthat as one of said coils moves more into said field the other coil willmove more out of said field, and vice versa, and circuit connections forconnecting vided circuit, the movements of said coils due to the currentin said circuit being independent of the strength of said current but afunction of the ratio in which it divides in said branches.

2. An electrical measuring instrument, comprising a magnet, a movingsystem com rising a plurality of current-carrying coils ocated outsideof a common axis and mechanically free to move therearound in the fieldof said magnet in such a manner that as one of said coils moves moreinto said field the other coil will move more out of said field and viceversa, and circuit connections for connecting said coils each in aseparate branch of a divided circuit, the movements of said. coils dueto the current in said circuit being independent of the strength of saidcurrent but a function of the ratio in which it divides in saidbranches.

. 3. An electrical measuring instrument,

comprising a magnet having facing polepieces; a moving system comprisinga plurality of current-carrying coils located outpieces;

side of a common axis and mechanically free to move therearound in thefield of said magnet in such a manner that as one of said coils movesmore into said field the other coil vwill move more out of said fieldand vice versa; circuit connections for connecting said colls each in aseparate branch of a divided clrcuit, the movements of said coils due tothe current in said circuit being independent of the strength of saidcurrent but a function of the ratio in which it divides in saidbranches; a resistance permanently in one of said branches in serieswith the moving coil in that branch; an indicator operated by saidmoving system, and a scale to cooperate with saidiindicator for directreading.

- 4; An electrical measuring instrument,

comprising a permanent magnet having polepieces crescent-shaped asherein described;

a moving system comprising two rigidly-connected flat current-carryingcoils located on difier'ent sides of a common axis and mechanically freeto move therearound in the field between said pole-pieces in ,such amanner thatas one of said coils moves more into said field the othercoil will move more out of said field and vice, versa, one of said coilsbeing tapped onto said connection between said coils, two additionalleads, one from the outer terminal of each of said coils; an indicatoroperated by said moving system, and a scale to cooperate with saidindicator, for direct reading. e

5. An electrical measuring instrument, comprising a magnet having facingpolea moving system comprising two rigidly connected current carryingcoils located outside of a common axis and mechanically free tomovetherearound in the field between said pole-pieces in such a mannerthat as one of said coils moves more into said field the other coil willmove more out of said field and vice versa; circuit connections forconnecting said coils each in a separate branch of a divided circuit,the movements of said coils d e to the current in said circuit beingindependent of the strength of said current but a function of the ratioin which it divides in said branches; an indicator operated by saidmoving system, and a scale to cooperate with said indicator for directreadmg.

6. An electrical measuring instrument, comprising a magnet having facingpolepieces; a moving system comprising two rigidly connected currentcarrying coils located outside of a common axis and mechanically free tomove therearound in the field between said pole-pieces in such a mannerthat as one of said coils moves more into said field the other coil willmove more out of said field and vice versa; circuit connections forconnecting said coils each in a separate branch of a divided circuit,the movements of said coils due .to the current in said circuit beingindependent of the strength of said current but a function of the ratioin which it divides in said branches; a resistance permanently in one ofsaid branches in series with the moving coil in that branch; anindicator operated by said moving system, and a scale to cooperate withsaid indicator for direct reading.

7. An electrical measuring instrument, comprising apermanent magnethaving polepieces crescent-shaped as herein described a moving systemcomprising two rigidly-connected fiat current-carrying coils located onop osite sides of a common axis and mechanica ly free to movetherearound inthe field too between said pole pieces in such manner thatas one of said coils moves more into said field the other coil Will movemore out of said field and vice versa; circuit connections forconnecting said coils each in a separate branch of a divided circuit,the movement of said coils due to the current in said circuit beingindependent of the strength of 'said .curr'entbut a function of theratio in which it divides in saidbranches; a resistance per- .manentlyin one of said branches in series with the moving coil in that branch;an indicator operated by said moving system, and a Y scale to cooperatewith said indicator for direct readin 8. An electrical measuringinstrument, comprisin a field-magnet having polapieces crescent-s apedas described; a movin system comprising two rigidly-connects fiatcurrent-carrying coils supported by andlo? cated on opposite sides ofand substantially equidistant from a common axis, said axis beingeccentric with the arcs forming the inner boundaries of the crescents ofsaid polenleces 9. An electrical measuring instrument, comprisini afield-magnet having pole-pieces crescent-s aged as described, asupportingaxis perpen 'cular to the pole-faces of said magnet, said axisbeing eccentric with the arcs forming the inner boundaries of thecrescents of said pole-pieces, a damping-frame comprising two lates ofnon-ma etic metal rigidly mounted on said axis and aving wings a apt- 10ed to encircle said pole-pieces as described,

and two flat current-carrying coils mounted between said plates andlocated on opposite sides of and substantially equidistant from saidaxis.

In testimony whereof I affix signature 1 5 in presence of two witnesses.

. EDWIN F. NORTHRUP.

Witnesses:

JULIUS BERNSTEIN, W. L. SWETLANR,

